Diapause in the nematodeGlobodera pallida

Abstract

Over a period of 12 months ‘new’ and ‘old’ cysts ofGlobodera pallida were hatched in potato root diffusate according to a novel ‘nematode-response’ hatching protocol. In this protocol, cysts were set to hatch at the beginning of autumn and then left to indicate when their hatching ability was exhausted (when less than 100 juveniles/replicate/week emerged) before another batch of cysts was set to hatch. At any time of the year for the 12 months this experiment was conducted there were cysts hatching. After 12 months of hatching, eight hatching curves were obtained. Based on the hatching curves of the ‘new’ and ‘old’ cysts, diapause was shown to be present in ‘new’ cysts in autumn, winter and early spring. However, diapause was absent in late spring and summer.

Infectivity assays to distinguish between juveniles obtained in the periods when cysts were in diapause and when cysts had overcome their diapause failed to show any significant difference in their infectivity. There was no significant difference in the number of eggs in ‘new’ and ‘old’ cysts. Based on this observation, it was suggested that high emergence in ‘old’ cysts may not be a result of few eggs in the cyst but rather due to absence of diapause. Also the presence of large numbers of eggs in ‘old’ cysts even after being stored for 12 months outdoors in the soil does not support the theories of spontaneous hatching, micro-organism induced hatching or persistence of hatching factors in the soil.